MySQL 如何查找一组列中具有空值的记录

为此，使用GREATEST()的概念。让我们首先创建一个表−

mysql> create table DemoTable1862
     (
     Value1 int,
     Value2 int,
     Value3 int,
     Value4 int
     );
Query OK, 0 rows affected (0.00 sec)

使用insert命令将一些记录插入表中−

mysql> insert into DemoTable1862 values(43,34,56,42);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1862 values(NULL,78,65,NULL);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1862 values(110,NULL,78,NULL);
Query OK, 1 row affected (0.00 sec)

使用select语句显示表中的所有记录−

mysql> select * from DemoTable1862;

这将产生以下输出−

+--------+--------+--------+--------+
| Value1 | Value2 | Value3 | Value4 |
+--------+--------+--------+--------+
|     43 |     34 |     56 |     42 |
|   NULL |     78 |     65 |   NULL |
|    110 |   NULL |     78 |   NULL |
+--------+--------+--------+--------+
3 rows in set (0.00 sec)

下面是查找一组列中具有空值的记录的查询语句−

mysql> select * from DemoTable1862 where greatest(Value1,Value2,Value3,Value4) IS NULL;

这将产生以下输出−

+--------+--------+--------+--------+
| Value1 | Value2 | Value3 | Value4 |
+--------+--------+--------+--------+
|   NULL |     78 |     65 |   NULL |
|    110 |   NULL |     78 |   NULL |
+--------+--------+--------+--------+
2 rows in set (0.00 sec)

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